Theoretical study of the neutral decomposition of SF₆ in the presence of H₂O and O₂ in discharges in power equipment

In the presence of H₂O and O₂, the dissociation products of SF₆ will decompose to form several main stable byproducts (i.e. SOF₂, SOF₄ and SO₂F₂) in an electrical discharge. These byproducts are chemically active and have been shown experimentally to be associated with discharge faults. However, the relationships between the discharges and types of decomposition components are still not clear, mainly due to the fact that the complex chemical processes during SF₆ discharges are not fully understood. In order to comprehensively investigate the decomposition of SF₆, an approach combining density functional theory (DFT) and transition state theory (TST) was used to study the pathways of SF₆ decomposition in mixtures with H₂O and O₂ that involve electrically-neutral species. The complex chemical reactions were analyzed, and the corresponding rate constants were predicted. The structural optimizations, vibrational frequency calculations and zero-point energy calculations of the species involved in each chemical reaction considered were carried out using the DFT-B3LYP method. Single-point energies were calculated using the CCSD(T) method. Based on the energy information obtained, the rate constants were predicted by TST, over a large temperature range, from 300 to 12 000 K.